30 



HELEN DEAN KING 



with the findings' of Darwin (1875) and others that under the 

 more favorable environmental and nutritive conditions of life 

 in captivity domesticated animals breed earlier and longer, 

 and are more prolific than their wild ancestors. 



FEETILITY 



Literature on the fertility of wild gray rats deals chiefly 

 with records of the young found in nests at different seasons 



TABLE 8 



Litter production and average litter size in different generations of captive 



gray rats 



of the year, and with data for the number of fetuses in gravid 

 females of unknown ages. Estimations regarding litter pro- 

 duction and litter size differ greatly. According to various 

 accounts (Zuschlag, '03; Lantz, '10; Miller, '11; Eaton and 

 Stirrett, '28), wild females produce an average of from three 

 to eight litters a year : litter size has been calculated as aver- 

 aging from six to ten young (Crampe, 1884; Zuschlag, '03; 

 Lloyd, '09; Lantz, '10; Miller, '11). 



